Downhole centraliser

Abstract

A downhole centralizer arranged to receive a downhole tubular has a tubular body with opposed ends and is formed of plastics material A respective end ring is mounted in the or each opposed end and is formed of a plastics material having a Youngs Moldulus no greater than that of the tubular body.

The invention claimed is: 
     
       1. A downhole centraliser arranged to receive a downhole tubular, the centralizer comprising:
 a tubular body having opposed ends and being formed of plastics material; and 
 at least one end ring mounted to an end of the tubular body, the or each end ring also being formed of a plastics material and having a Youngs modulus no greater than that of the tubular body, 
 at least one end of the tubular body having a relatively thin wall section arranged to receive an end ring wherein, the or each end ring comprises an annular member arranged to engage with an inner surface of a relatively thin annular wall section, the or each relatively thin wall section of the tubular body being provided with a plurality of spaced projections or apertures and the or each annular member being provided with a corresponding plurality of spaced apertures or projections, each aperture being arranged to engage with a corresponding projection such that the end ring and the body are positively engageable. 
 
     
     
       2. A downhole centraliser according to  claim 1 , wherein a respective end ring is mounted to each of the opposed ends of the tubular body. 
     
     
       3. A downhole centraliser according to  claim 1 , wherein the tubular body and the or each end ring are formed of the same plastics material. 
     
     
       4. A downhole centraliser according to  claim 1 , wherein the or each end ring is engaged with the tubular body by means of an interference fit. 
     
     
       5. A downhole centraliser according to  claim 1 , wherein the or each end ring is positively engageable with the tubular body in a releasable manner. 
     
     
       6. A downhole centraliser according to  claim 1 , wherein the or each end ring has an inner face formed with a plurality of spaced inward extending projections which are arranged in use to bear on a tubular member about which the centraliser is mounted. 
     
     
       7. A downhole centraliser according to  claim 1 , wherein there is provided a seat at an inner end of the thin wall section for engagement with the annular member. 
     
     
       8. A downhole centraliser according to  claim 1 , wherein the or each end ring has a small degree of resilience enabling it to be urged inwardly upon engagement with the body and then springing outwardly upon release. 
     
     
       9. A downhole centraliser according to  claim 1 , wherein the or each end ring and the tubular body are provided with cooperating alignment and anti-rotation means. 
     
     
       10. A downhole centralizer according to  claim 9 , wherein the cooperating alignment and anti-rotation means comprise a plurality of spaced slots on one member and a corresponding plurality of spaced ribs on the other member, corresponding said slots and ribs being arranged to be interengaged. 
     
     
       11. A downhole centralizer according to  claim 1 , wherein the downhole centralizer is substantially rigid. 
     
     
       12. A downhole centralizer according to  claim 1 , wherein the or each end ring is provided with a plurality of spaced projections whilst the or each inner wall section is provided with a corresponding plurality of spaced apertures. 
     
     
       13. A downhole centralizer according to  claim 12 , wherein the or each projection is asymmetrical in having a tapered inner portion and an angular outer portion. 
     
     
       14. A downhole centraliser arranged to receive a downhole tubular, the centralizer comprising:
 a tubular body having a first end with a thinned wall section and an inner surface, the tubular body being formed of a first plastics material, the inner surface having a plurality of spaced radial projections or apertures; and 
 a first annular end ring having an outer surface, the first annular end ring being formed of a second plastics material, the first annular end ring having a Youngs modulus no greater than a Youngs modulus of the tubular body, the outer surface having a corresponding plurality of spaced radial apertures or projections, 
 wherein the first annular end ring is mounted to the first end of the tubular body with the plurality of spaced radial projections or apertures of the inner surface positively engaging the corresponding plurality of spaced radial apertures or projections of the outer surface. 
 
     
     
       15. A downhole centraliser according to  claim 14 , wherein the tubular body further comprises a second end with the thinned wall section and the inner surface having the plurality of spaced radial projections or apertures, and further comprising a second annular end ring having the outer surface with the corresponding plurality of spaced radial apertures or projections, the second annular end ring being mounted to the second end of the tubular body with the plurality of spaced radial projections or apertures of the inner surface positively engaging the corresponding plurality of spaced radial apertures or projections of the outer surface. 
     
     
       16. A downhole centraliser according to  claim 14 , wherein the first and second plastic materials are a common plastics material. 
     
     
       17. A downhole centraliser according to  claim 14 , wherein the first annular end ring forms an interference fit with the first end of the tubular body. 
     
     
       18. A downhole centraliser according to  claim 14 , wherein the first annular end ring is releasably mounted to the first end of the tubular body. 
     
     
       19. A downhole centraliser according to  claim 14 , wherein the inner surface of the first end further comprises a seat for engagement with the first annular end ring. 
     
     
       20. A downhole centraliser according to  claim 14 , wherein the inner surface of the first end further comprises a plurality of spaced axial slots or ribs and the outer surface of the first annular end ring comprises a corresponding plurality of spaced axial slots or ribs, the plurality of spaced axial slots or ribs of the inner surface positively engaging the corresponding plurality of spaced axial slots or ribs of the outer surface.